body,html{
  margin:0;
  padding:0;
}
#main{
  margin:50px auto;
  width:260px;
}
#calc{
  margin-left:60px;
  width:60px;
  margin-bottom: 15px;
}
input{
  margin:5px 0;
}
span{
  color:red;
  margin-left:5px;
}
#width-validate,#height-validate{
  color:red;
  /* border: 1px solid red; */
  width: 203px;
  height: 13px;
  padding-left: 57px;
  font-size: 13px;
}
#perimeter{
  margin-bottom: 15px;
}
#area{
  margin-bottom: 15px;
}
input:invalid+span:after{
  content:'✖';color:red
}
input:valid+span:after{
  content:'✓';color:green
}